Mr McCrone said new legislation is required to give the Home Secretary the power to ban weapons like the Brocock air cartridge pistol when they become a threat to public safety.

Police want a ban on the public sale of the airguns

The pistols are imported and distributed by the Birmingham-based company Brocock, which makes the air cartridge system that powers the air gun pellets.

Brocock said in a statement: "Both the police and a Home Office ballistics expert confirm that we're already doing everything possible to prevent the illegal conversion of these products which are sold through a network of registered dealers."

Alan Shiers, an officer with the National Criminal Intelligence Service (NCIS), has been collating information from police forces across the country

He told BBC's Newsnight that conversion of Brococks amounted to a "major problem" which had to be tackled.

Special sleeves

He said: "We're having reports of this type of weapon being recovered not just in London where the problem started - but it's now spread to Manchester, Nottingham, Bristol, all over the country."

Figures from NCIS show that converted Brococks now account for 35% of all guns recovered by the police.

When used legally, the airgun fires small pellets using a compressed air charge in a cartridge that is loaded into the pistol.

Brocock air cartridge pistols are purchased by our customers for the legal
pursuit of their sport

Brocock, pistol importer

But criminal gangs have been adapting the guns by fitting special steel sleeves inside the chamber of the gun, enabling live .22 calibre bullets to be fired.